"Jesus Murillo Karam says an investigation by Mexican, Spanish, U.S. and British experts found no evidence of explosives in the blast that collapsed several lower floors of the Petroleos Mexicanos administrative building on Thursday afternoon.

"He said Monday that the experts believe that an electrical fault had caused a spark that detonated the leaking gas. There was scant evidence of the burn marks typical in a bomb blast, he said. There was also no sign of a crater like that typically left by an explosive device."

"The oil monopoly has been plagued for years by a horrendous accident record, widespread corruption and antiquated infrastructure. Oil output at the state monopoly has been falling and some experts say without the infusion of foreign investment, Mexico, one of the world's largest oil producer may be importing oil by 2018."